The present invention relates to a dual element ferrule fuse; were specifically, the present invention relates to a dual element fuse wherein the overload element has a heater element including integral tabs which center and index the overload element in the fuse and form a surface for attachment of the element to the end cap.
Dual element fuses are well known in the art and typically include a short circuit element as well as an overload element. The short circuit element usually includes at least one copper alloy or silver strip with weakened areas which melt with overload currents of over 700% of fuse rating. The overload element, installed in series with the short circuit element, includes a spring-loaded trigger with a copper alloy heating element. Upon sustained overload currents of 120-600% rated current, fusing alloy connecting the heater element to parts of the trigger and the trigger to the short circuit element will melt and a compression spring will separate parts of the trigger, thereby opening the electrical circuit.
In assembly, fusible elements are inserted into the fuse body and a terminating washer is placed between the overload element and the metallic end cap. Solder is applied within the end cap and pre-flowed for an even distribution within the cap. The end cap is then installed on the end of the fuse body and external heat is applied to melt the solder. In some cases, current is induced through the end cap, causing the solder to flow thereby connecting the end cap mechanically and electrically to the fuse element. In recent applications, some heater elements have themselves served as terminating washers. However, these integral washers have not been completely effective because they offer no way to keep the fuse element centered in the cap and held at a proper distance in relation to the end of the tubular body prior to soldering the element to the end cap.
There is a need therefore, for a dual element ferrule fuse wherein the heater element portion of the overload element provides a surface for connection of the overload element to the metallic end cap and also provides a means for centering the element in the cap between assembly and soldering of the element to the cap.
There is a further need for a dual element ferrule fuse wherein the heater element provides a surface for connection of the overload element to the end cap and also has means for retaining the element a relative distance from the other element in the fuse body prior to soldering of the cap to the element.